On tonight’s episode of Supernatural, we get a rare glimpse into Sam and Dean’s lineage, with the surprise introduction of their grandfather Henry (Gil McKinney), whom they only know as the man that abandoned their father, John (Jeffrey Dean Morgan).At a pre-screening of tonight’s episode, exec producer Bob Singer talked to Wetpaint Entertainment about the decision to introduce a new family member into the mix.Wetpaint Entertainment: What are the differences between Sam and Dean’s father, John, and their grandfather Henry?Bob Singer: John’s the product of the fact that he didn’t have a father growing up. So he always had a grudge against his father because he thought [his father] deserted him. We wanted to [introduce Henry] because we’d spent time with the other side of the family, and [we wanted] to bring it full circle. Now we know who the grandfather is on [John’s] side of the family and why John became what he was. It was supposed to be something different.Were you looking for physical similarities in casting the role?Not really. It was a generation removed. We were looking the best actor to work with the boys and also for a contrast. This was a guy that was more elegant, more educated. We were looking for more of a contrast than a sameness.What can you say about Dean’s feelings about his grandfather?I think he’s like, “Do I really need this guy popping out of my closet, bringing up this whole dad thing? Now I’ve got to have mixed emotions about this guy.” Henry was not the nicest guy to them — he’s tolerating them.But in the end you wanted to make their grandfather a nice guy.It felt right to us — the idea of them meeting their grandfather and understanding that the knowledge that they’ve carried all their life [was knowledge that John’s] dad left — and how John became the guy that he was is all untrue, all the anger he carried was not real. It has a certain pathos to it. And I think one of the reasons we’ve lasted so long is because we tell these personal stories. Whatever the plot of the week is, it ultimately comes down to how are the brothers feeling about it — how does it affect their relationship? What’s underneath the surface of the story?Supernatural airs tonight, Wednesday, January 30, at 9 p.m. ET on The CW.